The electrical activity of neurons and other cells is regulated by the flow of ions across the cell membrane via a special class of membrane proteins known as ion channels. Protein phosphorylation is an important mechanism for the modulatory regulation of ion channels, and is a potential target for therapeutic agents. While the effects of serine/threonine phosphorylation of ion channels have been investigated extensively, the role of tyrosine phosphorylation of ion channels is largely unexplored. The goal of this proposed project is to investigate the mechanisms of tyrosine phosphorylation of the voltage gated potassium channel Kv1.3 in a heterologous mammalian expression system. Sequence analysis of Kv1.3 shows that this channel contains several tyrosine residues which are potential kinase targets. My preliminary data indicate that Kv1.3 expressed in HEK293 cells is tyrosine phosphorylated by endogenous tyrosine kinases. Furthermore, co-expression of Kv1.3 and the tyrosine kinase v-src leads to large increases in Kv1.3 tyrosine phosphorylation. I propose to extend these preliminary findings and further my training by: (1) determining the mechanism(s) for kinase/channel recognition and specificity; (2) identifying by site- directed mutagenesis the tyrosine residues in Kv1.3 which are targets for phosphorylation; and (3) collaborating with electrophysiologists to elucidate the functional consequences of tyrosine phosphorylation of Kv1.3.